This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A170815 #3 Mar 31 2012 12:35:36 %S A170815 1,2,4,12,40,116,200,444,760,2160,4368,7852,12828,17252,19612,21104, %T A170815 18276,15096,10240,6464,3776,2536 %N A170815 Number of permutations of 1..n with all differences of elements separated by distances 1 through 9 being respectively unique. %C A170815 (Empirical) Equals A008404 for n<=2m+2, where m is the maximum difference separation 9. %K A170815 nonn %O A170815 1,2 %A A170815 _R. H. Hardin_ Dec 02 2009